The food and drink giants behind the £4m ad campaign promoting GDA front-of-pack labelling have rubbished allegations that they are attempting to derail the FSA's traffic-light system - or that GDAs are difficult to understand.

The 18-month campaign, backed by the FDF, 21 suppliers and three major retailers, starts on Monday with a TV ad urging consumers to 'Know what's going inside you'.

The launch will be followed by print and digital media campaigns focused on helping consumers to make choices and comes ahead of a rival FSA campaign promoting traffic lights later this month. "We should feel good so many people are committed to front-of-pack labelling," said Ben Clarke, vice president and area director of Kraft Foods UK & Ireland. "Equally we shouldn't be surprised that different people support different schemes." Campaign director Jane Holdsworth added: "The point to stress is the similarity between the two schemes. They're both front-of-pack, both tell consumers really clearly how much of certain nutrients there are in a product."

However, she warned, traffic lights could be misleading because they focused on high, medium or low levels per 100g rather than on how a product fitted into a diet. GDAs were more easily applied to a wide range of categories than traffic lights, which were originally intended to cover just a few, she added.

GDAs have already been adopted by 40% of the market, representing 10,000 lines, and the aim was to double that by next year, said Holdsworth.

More than 70% of shoppers were aware of GDA labels and half already used them accurately and easily, she added, citing research by Millward Brown.